To implement a coordinated program of research into use of antiretroviral (ARV) therapy and the reduction of risk behavior in resource constrained (Thailand) and resource limited (Cambodia) settings. The primary theme of this program is the appropriate and cost-effective use of ARV therapy in developing countries. Specific Aims 1. To assess strategies for inexpensive and logistically simple monitoring of ARV therapy 2. To compare strategies of immediate versus delayed treatment of HIV-infected children in resource limited settings 3. To assess the optimal timing for initiation of ARV therapy in the management of HIV/TB co-infection 4. To investigate behavioral interventions for the reduction of risk behavior and HIV transmission in patients treated with ARV therapy 5. To link the projects using a family unit recruitment strategy 6. To strengthen clinical and prevention research capacity in Thailand and Cambodia 7. To guide clinical and public health policy in Thailand and Cambodia Methods The proposed CIPRA program will investigate treatment and behavioral interventions that will inform public health policy in Thailand, Cambodia and other countries of the region. The research methodologies to be used are randomized clinical trials and observational cohorts. The individual projects involve multiple recruitment sites in Thailand and Cambodia. In the course of conducting this research, training will be provided to strengthen the capacity of Thai and Cambodian investigators and health professionals in the conduct of clinical and public health research. The projects will be linked by a family recruitment strategy.